1. Field of the Invention
The present invention relates to a method for correcting focus in an aligner (stepper) and a method for manufacturing semiconductor devices by using an aligner in which focus is corrected by the focus correcting method.
2. Description of the Background Art
Conventionally, the management of focusing of aligners includes the focus calibration performed several times a day (the management in which the distance between the stage and reticle is measured and the variation is fed back to focusing in exposure), the best focus check performed several times a month by forming resist pattern by using a test reticle (the management in which resist pattern is formed and the deviation of the present focusing value from the best focus is calculated by viewing, or by measuring dimensions of the test pattern and is fed back to the aligner), and the leveling function check (the management in which the inclination of the wafer plane and the image plane of the shots in the aligner is measured and adjusted). These management processes are too time consuming to perform frequently, and therefore periodical variation of focus of the aligner having several-hour or shorter cycle cannot be followed, which leads to increased variation of the resist pattern due to defocusing.
As conventional aligners, for example, Japanese Patent Laying-Open Gazette No.9-92606 discloses a device which adjusts focus on the basis of correction data obtained from level marks formed on the wafer, Japanese Patent Laying-Open Gazette No.5-190419 discloses a device which adjusts focus by using test pattern formed on a test substrate, and Japanese Patent Laying-Open Gazette No.7-86135 discloses a device which adjusts focus with weighted focus information to compensate for phase lag of focusing signal.
In the conventional focus correcting methods performed as stated above, it is difficult to measure the focus deviation, and therefore the focus deviation cannot be measured for each lot manufactured in short cycle so that the measured deviation can be utilized for the next lot, which raises the problem of difficulty in improving the focus correcting accuracy.